1. Field of the Invention
The present invention relates generally to the fields of optical imaging and medical diagnosis. More specifically, the present invention relates to an apparatus and means for non-invasively measuring the movement of various parts of the human body, most notably thoracoabdominal movement associated with breathing.
2. Description of the Related Art
There are a variety of conditions whereby unambiguous, quantitative measurements of the movement of human anatomical structures would be of diagnostic benefit. For example, the presence and magnitude of hand tremor is associated with certain neurologic and muscular disease processes. Specific parameters of rapid e y e motion (REM) during certain phases of sleep is diagnostic of some abnormal conditions. The rate and relative movement of the thorax that is associated with breathing also provides potentially important diagnostic information, such as presence of asthma or other respiratory diseases, airway blockage, or other abnormal lung function.
The societal and financial cost to health care infrastructure and the economy as a whole as a consequence of respiratory disease is immense. Newacheck and Halfon (1) determined that approximately 6.5% of all children in the United States, experienced some degree of disability, with the most common causes of being respiratory diseases and mental impairments. This results 24 million days lost from school and in an added 26 million physician contacts and 5 million hospital days annually. In an earlier study (2), investigators found that the prevalence of asthma in children younger than 18 years of age in the United States was 4.3% in 1988 and was 3.2% in 1981 resulting in 12.9 million contacts with medical doctors, and 200,000 hospitalizations. The 10% of children with severe asthma accounted for 35% of hospitalizations and 77% of the days in the hospital. Chronic conditions such as asthma result in a huge burden to the economy of the United States. In fact, more than 90 million Americans live with chronic conditions (1, 2), which include diabetes and heart disease as well as asthma. Respiratory disease accounts for, or is associated with, as much as 10% of chronic disease, resulting in healthcare costs in excess of $65 billion annually.
Respiratory disease is the number one cause of morbidity and mortality in infants worldwide. Measurements of lung function (e.g. tidal volume, VT, which is the volume change from the peak expiration volume to the minimum inspiration volume) give insight into the respiratory status of humans. Other breathing indices give further clinical information; for example, the time to peak expiratory volume (tPTEF) combined with total expiratory time (tE) provides information on airway caliber. Respiratory frequency, fR, is the most utilized variable of breathing pattern in clinical practice, and provides diagnostic information on cardiorespiratory and systemic disease, pneumonia, sepsis, congestive heart failure, etc. Thoracoabdominal asynchrony in movement also provides important clinical information, especially in infants.
In infants and children, measurement of VT is usually done with a pneumotachygraph (PNT), which involves attaching a facemask to the infant. This method causes subject anxiety and results in a transient, but long-lived increase in fR and decrease in VT. In fact, simply touching the infant results in stress, causing significant changes in many physiologic parameters. A non-contact means of measuring lung function would eliminate stress associated with manipulation of the patient while measuring respiratory function, and, therefore would provide data of greater clinical relevance.
Quantification of chest wall movement has long been regarded as clinically useful for measurements of amplitude, thoracoabdominal asynchrony, frequency, etc. In 1993, the Joint Official Statement by the American Thoracic Society and the European Respiratory Society on Respiratory Mechanics in Infants stated, xe2x80x9c . . . little is known about the infant chest wall . . . chest wall mechanics should be studied in infants with neuromuscular disease, chest wall abnormalities, and primary lung disease, and the role of chest wall instability in overall respiratory pump malfunction should be assessed . . . chest wall motion should be investigated as an indicator of control of breathing.xe2x80x9d
Techniques to measure the motions of anatomic structures often make use of accelerometers or other mechanical transducers. The disadvantages with using these devices are their inherently low spatial resolution, extensive calibration procedures, and most of these devices must be operated in a contact mode. Mechanical arms and such that are in contact with the anatomic structure and have rotation and displacement transducers can b e used to measure movement, but these devices are cumbersome and require contact between the device and subject.
Other techniques to measure motions make use of rangefinders. For example, single lens reflex cameras use contrast maximization of an image to determine range. Ultrasound pulses and time-of-flight measurements are also used to detect motion as are changes in magnetic field strength which can further be used to determine the location of sensors. Another type of rangefinder involves projecting a pattern on the object in question, imaging the pattern shape and changes with time, and then calculating movement.
Because of the importance of being able to measure specifically the movement of the chest and abdomen, considerable effort has been expended to develop good methodologies and devices. For example, strain gauges, incorporated in straps positioned around a partial circumference of the infant, stretches during breathing, thus producing an electrical signal which can b e monitored. This method has limitations in that placement of the strap alters the readings, and the strap itself changes the compliance of the chest and abdomen thus affecting the reading. Magnetometers and changes in impedance have also been used with various degrees of success. All of these methods suffer from being unable to detect spatial non-uniformity in thoracoabdominal movement.
Since 1985, the respiratory inductive plethysmograph (RIP) has been the most commonly used monitor of thoracoabdominal movement. This device makes use of changes in inductance due to movement of coils of wire incorporated into cloth bands placed on the rib cage and abdomen. This technique is based on the determination that the total volume changes upon respiration are equal to the sum of the volume changes in the ribcage and abdomen. While the respiratory inductive plethysmograph has proven to be useful, it is difficult to calibrate, inconsistent with simultaneous measurements using strain gauges and magnetometers, and furthermore still involves disturbing the infant by the placement of the transducers on the chest and abdomen.
Several groups have investigated optical means in an effort to develop a non-contact way of monitoring thoracoabdominal movement. Laser speckle interferometry has been documented and a method based on quantifying the alteration of a pattern of markers projected on the chest has been tested. (3, 4). Aubert, et al., (5) and more recently a group in Australia (6) have tested the idea of using an optical rangefinder to monitor chest wall movement. Aubert et al. measured chest wall movements associated with the heartbeat, which were between 0.3 and 0.8 mm. Torsten et al. showed that measurements of VT and abdominal wall displacement correlated well with an independent measurement of end-expiratory lung volume. In both of these cases, ambiguity as a consequence of measuring a single point was problematic, and the use of the device in ambient lighting also presented a further complication.
None of the optical methods for measuring lung function have made the transition from the laboratory to an FDA approved clinical device. Note, however, that Cala and co-workers (7) very accurately determined lung volumes by optical reflectance motion analysis whereby 86 reflective markers were positioned on subjects and were imaged by video cameras. Based on geometric considerations, and using a surface triangulation method for volume calculations, they clearly showed that it was possible to accurately ( less than 2% error) determine tidal volume; no calibration factor was required to correlate these data to spirometer readings.
The prior art is deficient in the lack of an optical apparatus and effective means for measuring the movement of anatomical structure non-invasively, especially for measuring thoracoabdominal movement associated with breathing. The present invention fulfills this long-standing need and desire in the art.
The present invention is directed to an apparatus and means for non-invasively measuring the real time movement of external or internal body parts, thereby improving the diagnosis of, for example, respiratory disease and the monitoring of therapy. The apparatus is inexpensive, portable, non-contact, simple to use, and can be configured to work through an endoscope.
In one embodiment of the present invention, there is provided a method for measuring body movement of a tissue of interest, comprising the steps of emitting radiant energy to the surface of the tissue to form a spot; detecting an image of the pattern of radiant energy reflected from the spot, wherein the pattern corresponds to the position of the spot relative to the source of the radiant energy; and determining the pattern change with time, wherein the pattern change corresponds to the change of the spot position relative to the source of radiant energy, thereby indicating the body movement of the tissue.
In another embodiment of the present invention, there is provided an apparatus for detecting movement of an anatomical structure, comprising a source of radiant energy; a means for projecting the radiant energy in a pattern over a region of interest in the anatomical structure and a means for detecting change in the pattern of radiant energy reflected from the region of interest. Such apparatus can be used for monitoring sudden infant death syndrome (SIDS), evaluating rapid-eye-movement (REM) sleep and other clinical purposes.
Other and further aspects, features, and advantages of the present invention will be apparent from the following description of the presently preferred embodiments of the invention given for the purpose of disclosure.